Field
The present disclosure relates to telecommunications apparatus and methods. In particular certain examples of the disclosure relate to telecommunications apparatus and methods using relay nodes to relay data from terminal devices to network infrastructure equipment, such as a base station.
Description of Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Mobile communication systems have evolved from the GSM System (Global System for Mobile communications) to the 3G system and now include packet data communications as well as circuit switched communications. The third generation partnership project (3GPP) has developed a fourth generation mobile communication system referred to as Long Term Evolution (LTE) in which a core network part has been evolved to form a more simplified architecture based on a merging of components of earlier mobile radio network architectures and a radio access interface which is based on Orthogonal Frequency Division Multiplexing (OFDM) on the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.
Third and fourth generation mobile telecommunication systems, such as those based on the 3GPP defined UMTS and Long Term Evolution (LTE) architectures, are able to support a more sophisticated range of services than simple voice and messaging services offered by previous generations of mobile telecommunication systems. For example, with the improved radio interface and enhanced data rates provided by LTE systems, a user is able to enjoy high data rate applications such as mobile video streaming and mobile video conferencing that would previously only have been available via a fixed line data connection. The demand to deploy third and fourth generation networks is therefore strong and the coverage area of these networks, i.e. geographic locations where access to the networks is possible, is expected to increase rapidly.
To help improve the performance and flexibility of wireless (“mobile”) communications systems, relay nodes/devices can supplement transmissions associated with base stations. In particular relay nodes may be used to enhance coverage, either by extending coverage to new geographic areas or by enhancing the coverage at locations in an existing cell.
A relay node maybe considered as being distinct from a conventional cellular base station (e.g. a so-called eNodeB (eNB) in 3GPP LTE nomenclature) in the sense that a relay node may be wirelessly connected to the RAN (radio access network) through a conventional base station. The base station through which a relay node connects to the RAN is often referred to a donor base station/donor eNB (i.e. the term donor base station may be used to refer to a base station serving a relay node). The radio network cell supported by the donor eNB in which the relay node is located may similarly be referred a donor cell for the relay node.
In a 3GPP context, there are two main types of relay node, namely Type-I relays and Type-II relays. Type-I relays are a kind of non-transparent relay with wireless backhaul to the donor eNodeB cell. A Type-I relay has its own cell and physical cell identification (ID), terminates layers 2 and 3 protocols, and appears to a terminal device as a conventional base station. Therefore a Type-I relay, which transmits synchronization signals and performs resource allocation, can help to support a remote terminal device that is out of normal coverage of a base station, thereby extending the signal and service coverage. Type-I relays can operate in either an inband manner (with base station to relay node communications on the same carrier frequency as the relay node to terminal device communications) or an outband manner (with base station to relay node communications not on the same carrier frequency as the relay node to terminal device communications). A Type-II relay, on the other hand, does not have its own cell ID and the terminal device is not aware of whether or not it is communicating with the base station via the relay node (i.e. type-II relays are a kind of transparent relay). Type-II relay nodes support only inband operation.
Relay nodes may be distinguished from wireless repeaters. The function of a wireless repeater is simply to boost the power of the signals it receives. Wireless repeaters do not discriminate between wanted signal, interference or noise, and will re-broadcast all signal components received. Relay nodes, on the other hand, are regenerative repeaters in the sense that they decode a received signal and selectively re-broadcast appropriate components. Relay nodes can therefore provide for improved signal-to-noise ratios (SNRs), provided a signal is received at the relay node with a sufficient SNR to allow the relay node to decode it successfully.
One particular area in which relay nodes may be expected to be relevant is in the support of so-called machine type communication (MTC) applications. MTC applications are in some respects typified by semi-autonomous or autonomous wireless communication devices (MTC devices) communicating small amounts of data on a relatively infrequent basis. Examples include so-called smart meters which, for example, are located in a customer's home and periodically transmit data back to a central MTC server relating to the customer's consumption of a utility such as gas, water, electricity and so on. Smart metering is merely one example MTC application and there are many other situations in which MTC-type devices might be used, for example for traffic surveillance, e-healthcare and general monitoring applications. In general, MTC devices may be useful whenever there is a desire for devices to communicate wirelessly with some degree of autonomously (i.e. without human invention). Some typical characteristics of MTC type terminal devices/MTC type data might include, for example, characteristics such as low mobility, high delay tolerance, small data transmissions, infrequent transmission and group-based features, policing and addressing. Further information on characteristics of MTC-type devices can be found, for example, in the corresponding standards, such as ETSI TS 122 368 V11.6.0 (September 2012)/3GPP TS 22.368 version 11.6.0 Release 11) [1].
It can be expected that some types of terminal device, such as MTC type terminal devices, may in particular benefit from relay node support. For example, it can be expected that MTC devices will be relatively low-cost devices and might need to rely on battery power for extended periods. As such, it would be a benefit for such terminal devices to communicate with a base station via a nearer relay node to reduce the uplink transmission power required. Also, it can be expected that certain types of terminal devices, such as smart meter type devices, may be in locations with relatively high penetration loss (for example in the basement of a building). To address these issues there have been proposed schemes for coverage enhancement, for example based around power boosting of base station transmissions. However, to help address this issue on the uplink side, it may be expected that relay nodes will play an important role in coverage extension for certain types of terminal device, such as MTC type terminal devices.
Accordingly, there is a need for schemes for efficient handling of communications, for example in terms of reducing overall signalling overhead, in wireless telecommunications systems using relay nodes/devices to support communications between terminal devices and base stations.
There have been proposed schemes for multiplexing data from different users at a relay node to seek to improve resource utilization, such as by Teyeb, Oumer, et al. in “User multiplexing in relay enhanced LTE-advanced networks”, Vehicular Technology Conference (VTC 2010-Spring), 2010 IEEE 71st. IEEE, 2010 [2] and by Marwat, Safdar Nawaz Khan, et al. in “A Novel Machine-to-Machine Traffic Multiplexing in LTE-A System using Wireless In-band Relaying.” Mobile Networks and Management, Springer International Publishing, 2013. 149-158 [3], but these do not provide completely satisfactory solutions to at least some of the issues that can arise.